HVACR Tech Tip: Understanding Heat Pump Systems and Thermostatic Expansion Valves

Manufacturers have been successfully applying Parker Sporlan Thermostatic Expansion Valves on Heat Pump Applications for many years. Parker Sporlan's large diaphragm and durable welded element result in unmatched thermostatic expansion valve quality and life. In this blog we discuss using thermostatic expansion valves on different types of heat pump systems.

Conventional thermostatic expansion valve on heat pumps

Many variations and matches of expansion devices have been used to regulate flow to the evaporator coils of a heat pump system. Optimum control is achieved by employing two thermostatic expansion valves, one to feed each coil as shown in Figure 1. Each valve can be tuned to control desired super­heat for uniquely different coils and operating conditions.

The durable construction of the standard Parker Sporlan valve is ideal for heat pump applications. It is recommended that the external equalizer be connect­ed to the common suction line, as shown in Figure 1. The underside of the diaphragm will be exposed to high side pressures if the equalizer is connected to the suction line ahead of the reversing valve. Parker Sporlan diaphragms can withstand these pressures but discharge pulsations are a possible source of problems. Discharge pulses can be dampened but the OEM tests should be performed to prove reliability. When using a thermostatic expansion valve to con­trol flow in one direction only, as shown in Figure 1, there are two options available:

1. Employ a standard Parker Sporlan valve and install a bypass check valve for reverse flow.
2. Install a Parker Sporlan valve which incorporates an internal check valve that minimizes reverse flow pressure drop. There are two Parker Sporlan valves which incorporate this check valve feature. The RC valve and the CBBI valve. The CBBI valve is only available to OEM customers whereas the RC valve is also available to wholesalers. These valves are available for capacities through a nominal 6 tons, R-410A. 

Bi-Directional thermostatic expansion valves on heat pumps

The "Bi-Directional" Thermostatic Expansion Valve has successfully been used to replace two expansion devices as shown in Figure 2. It controls refrigerant flow to either coil when the coil is serv­ing as the system evaporator. The Bi-Directional valve is generally applied on packaged units with close coupled components. The bulb and external equalizer are mounted to the common suction line. The suggested flow direction for the Bi-Directional valve is with the valve flowing in its normal direc­tion when the system is in the heating mode. This flow direction will normally result in a lower superheat in the heating mode. The preferred flow direction for each application should be verified by test­ing. There are two valves which have been designed for Bi-Directional applications. The ER valve which is available to wholesale customers and the BBI valve which is only available to OEM customers. These valves are available in capacities through a nominal 15 tons, R-410A.

For more information on Parker Sporlan Thermostatic Expansion valves please see Bulletin 10-10. For selecting your appropriate valve configuration, visit our webpage.

For more information on applying filter-driers in the same heat pump system please see Bulletin 240-10-2.

HVACR Tech Tip Article contributed by Jason Forshee, application engineer,  Sporlan Division of Parker Hannifin

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